Exploring the Aggregation Mechanism of Graphene Oxide in the Presence of Radioactive Elements: Experimental and Theoretical Studies

In this study, the aggregation kinetics, aggregate morphology, and aggregation mechanisms of graphene oxide (GO) in the presence of Cs ⁺ , Sr ²⁺ , UO ₂ ²⁺ , Eu ³⁺ , or Th ⁴⁺ are characterized by using time-resolved dynamic light scattering, transmission electron microscopy (TEM)-element mapping, redispersion of GO aggregates, and density functional theory (DFT) calculations. The destabilization capability of Cs ⁺ , Sr ²⁺ , UO ₂ ²⁺ , Eu ³⁺ , and Th ⁴⁺ and the corresponding values of the critical coagulation concentration (CCC) are obtained for the first time. Polyacrylic acid is used as a dispersant to investigate the reversion of GO aggregates induced by various radioactive elements. The combined results of the poly(acrylic acid) effect and TEM-element mapping show that Cs ⁺ induces the aggregation of GO through electric double-layer suppression and weak binding with oxygen-containing functional groups. By employing DFT calculations, we find that the electrostatic potential distribution and the charge transfer rather than coordination with oxygen-containing functional groups control the destabilizing ability of radioactive elements with a higher valence. A comprehensive process of experimental and theoretical studies is considered to better elucidate the colloidal behavior, self-assembly process, application as a novel adsorbent, and environmental risks of GO.